The invention relates to a knee restraint device for vehicles.
In addition to the known safety restraint devices of airbag and belt, active knee restraint devices are being used increasingly in order to prevent the vehicle occupant from slipping through into the foot well, in particular when the occupant is not wearing his belt or is not occupying an optimum sitting position.
A generic knee restraint device is known from EP 0 872 388 A2. Therein, a knee restraint device is described, in which a knee protector part is moved in the case of restraint by an inflatable airbag toward the knees of the vehicle occupant. The knee protector part consists here of a rigid load distributor plate of metal, which is embedded into an elastic plastic material. The load distributor plate helps the knee protector part to get to the necessary stability and through deformation takes up kinetic energy from the knees of the vehicle occupant, whilst the elastic plastic material serves as padding. The knee protector part is fastened detachably by means of separate fastening pins to the instrument panel or to the base plate of the airbag unit. Through the embedding of the metallic load distributor plate into the elastic plastic material, the various materials can only be separated again with relatively high expenditure during a disposal which is later necessary. The use of separate fastening pins for fastening the knee protector part adds a further material to the assembly and requires furthermore additional expenditure on installation of the knee protector part. As the knee protector part is arranged in the visible area of the instrument panel, the covering must be adapted to the visual appearance of the instrument panel.
The invention is based on the problem of providing a knee restraint device, in which the covering of the knee protector part is connected simply and at a favorable cost with the load distributor plate. With regard to the disposal of old vehicles, required by legislation, an easy separability of the materials which are used is to be provided.
The above-mentioned requirements to be met are fulfilled by the knee restraint device according to the invention which comprises a base plate and a knee protector part fastened to the base plate. The knee protector part has a load distributor plate with openings and has a covering of plastic. The covering has a rear face facing the load distributor plate and a front face directed in an opposite direction. The covering is provided with pins formed on the rear face and is fastened in a form-fitting manner to the load distributor plate by the pins projecting through the openings in the load distributor plate. The pins have free ends which are shaped such that the free ends project radially outwards and over the openings.
Through the fact that the load distributor plate is not encased by the covering, the materials can be separated again later in a simple manner. By the pins being formed on the covering, a unit consisting of pins, i.e. fastening means, and a covering is produced. No separate fastening means is provided, which would accordingly have to be supplied separately during the assembly of the knee protector part and would have to be removed from the knee protector part on recycling. Hence, fewer components and also fewer different materials are provided than in the prior art. Furthermore, the fastening is very simple, because the pins only have to be shaped at their free end, which can take place in a very simple manner by the effects of temperature and/or pressure.
According to a preferred embodiment, the covering is produced from thermoplastic plastic and the pins are shaped under the action of heat. The free end of the pin can have a thickening or can also only be bent, in order to project radially with respect to the openings and project over the openings in the radial direction. The shaping of the free end can take place for example by means of ultrasound. The production of the knee protector part can take place in that firstly the covering and the load distributor plate are produced separately and the covering is subsequently fastened to the load distributor plate, by the pins being inserted through the openings and being shaped at their free ends. Another possibility consists in firstly embedding the load distributor plate by injection,s molding or foaming with a plastic, the pins also being formed by injection-molding or foaming and in so doing being given their final form together with outwardly projecting free ends.
According to the preferred embodiment, the knee restraint device is provided as an active restraint device, by an expansion device between the knee protector part and the base plate moving the knee protector part toward the knees in the case of restraint.
Some of the pins can be passed through openings in the base plate and shaped on the rear face thereof, whereby the knee protector part is fastened to the base plate. By selection of the radius of the pins or the type of plastic material, it can be achieved that the knee protector part detaches itself from the base plate with a force which is largely able to be determined in advance.
According to another embodiment of the invention, openings are provided in the base plate or the load distributor plate, through which fastening elements, arranged on the knee protector part, project, the marginal region of the openings defining radially inwardly projecting tongues and the fastening elements engaging behind the base plate or the load distributor plate at least in a partial region of the marginal region. The marginal region is constructed such that it is deformed in the case of restraint by the fastening elements and the fastening elements detach themselves from the base plate or load distributor plate. Pins formed on the covering could be part of the fastening elements in this embodiment.
Through the use of a metallic load distributor plate and a metallic base plate, the extent of the necessary forces for detaching the knee protector part remains largely independent of temperature and aging, because the mechanical properties are approximately constant in the required temperature ranges.
The types of fastening of the covering on the load distributor plate are independent of the types of fastening of the knee protector part on the base plate. The load distributor plate and the base plate are connected with each other by means of at least one bolt. This connection is destroyed on activation of the expansion device by the force exerted on the knee protector part by the expansion device, for the knee protector part to be able to move toward the knees. Where possible, this destruction of the connection should take place with forces which are able to be exactly determined in advance. Also, no flying individual parts should be produced.
According to one embodiment, the bolt is destroyed on activation of the expansion device; for this purpose, the bolt may be provided with a predetermined breaking site, for example. Furthermore, the bolt may also detach itself from the base plate or the load distributor plate and may remain fastened in the other part.
One embodiment provides that the bolt is a threaded bolt on which a nut is screwed. The bolt and/or the nut are fastened to the load distributor plate or the base plate and may be beaten into, bonded with or, for example, pressed into the respective plate for this purpose. It is further possible to reshape the bolt after fastening, by riveting, upsetting or pressing it so as to obtain a form-fitting connection. The bolt may be a steel bolt or also an aluminum bolt, for example. If a nut is screwed on the screw bolt, the screw bolt may have an increased roughness on the underside of its head, such as in the form of a set of teeth, which prevents rotation of the screw bolt when the nut is screwed on.
According to another embodiment provision is made that the base plate and the load distributor plate are bonded to each other such that the connection is destroyed on activation of the expansion device by the force it exerts on the knee protector part. This bonding connection can be produced for example by means of epoxy resin, an anaerobic adhesive and/or sealing compound, cyanoacrylate, silicone, or, e.g., polyurethane.
The bonding connection permits greater freedom of configuring the geometry of the load distributor plate and the base plate than a form-fit.